Hydraulic service jacks of the type used in lifting vehicles are well known. Such jacks commonly include a hydraulic cylinder and a hydraulic pump adapted to be manually driven so as to selectively force hydraulic fluid into the hydraulic cylinder. Examples of prior art hydraulic service jacks are set forth in the Flanagan U.S. Pat. No. 1,767,124 issued June 24, 1930; the Shevlin U.S. Pat. No. 1,784,116, issued Dec. 9, 1930; the Eason, et al. U.S. Pat. No. 1,978,451, issued Oct. 30, 1934; the Mueller U.S. Pat. No. 2,629,583, issued Feb. 24, 1953; and the Jakob U.S. Pat. No. 1,799,298, issued Apr. 7, 1931.
In some of the prior art service jacks such as those shown in the Eason U.S. Pat. No. 1,978,451 and the Mueller U.S. Pat. No. 2,629,583, the hydraulic pump is operable only when the jack handle of the service jack is in a nearly horizontal position and wherein the free end of the jack handle is close to the ground. Since the pumping action of the jack handle with the jack handle close to the ground is inconvenient to the operator, more modern service jacks have been designed with a hydraulic fluid pump arrangement specifically constructed to permit a pumping operation with the jack handle in a more vertical or raised position. The pump constructions of these jacks have the disadvantage of causing a lateral load to be placed on the piston of the hydraulic pump, thereby causing wear of the pump piston and the pump cylinder wall.